3. Add all the time intervals for each corresponding "n" together. This will give you an approximate time only. This initial estimate gives a generous amount of time that may exceed that of the actual time it might take to finish the song. However, factors such as:

..Also, do not forget to convert the time to years, months, days, hours, minutes, seconds if you want a better estimate to schedule your life activities.

Here is my own calculation:

a)I first calculated how long it takes to say each worded verse:
"...bottles of beer on the wall." = 3 seconds
"...bottles of beer." = 2 seconds
"...if one of the bottles should happen to fall." = 3 seconds
Since the first verse occurs twice, it must be counted twice.